This invention relates to a valve timing control device for varying the timing of opening and closing of intake and exhaust valves of an internal combustion engine in accordance with an operating condition of the engine, and more particularly to such a valve timing control device of the type which effects a valve timing control by means of hydraulic pressure.
A valve timing control device is disclosed, for example, in Japanese Patent Unexamined Publication No. 63-131808, in which in order to vary a valve timing of intake and exhaust valves in accordance with an operating condition of an internal combustion engine, within a hub of a timing pulley which is loosely fitted on a camshaft and is driven by a crankshaft through a timing belt, the timing pulley and the camshaft are provided with helical splines which are engaged with helical splines formed on at least one of the inside and outside of a tubular gear which is adjustably moved in an axial direction by a hydraulic pressure, and by moving the tubular gear back and forth in the axial direction by the hydraulic pressure, the timing pulley and the camshaft are rotated relative to each other.
In this conventional device, a hydraulic control valve is provided at the internal combustion engine body remote from the valve timing control device, and since pressurized oil needs to be supplied to a pair of hydraulic chambers provided respectively on the front and rear sides of the tubular gear, two oil passages are formed in a journal portion of the camshaft. As a result, not only the construction of the oil passages becomes complicated, but also in order to install the valve timing device, the camshaft, the journal portion and etc., of the internal combustion engine need to be extensively modified. And besides, the distance between the hydraulic control valve and each of the pair of hydraulic chambers is great, and they are interconnected by the oil passage formed in the journal portion of the camshaft and other portions, and therefore it is thought that a problem with respect to the response and reliability of the control is liable to arise.
To deal with this problem, Japanese Patent Unexamined Publication No. 2-271009 proposes a construction in which a hydraulic control valve is formed integral with a main portion of a valve timing control device. In this construction, however, since the hydraulic control valve is provided at an axial end portion of a camshaft, the overall length of the valve timing control device becomes great because of the provision of the hydraulic control valve. Therefore, there is produced a problem that a relatively large space is required for mounting the valve timing control device on the internal combustion engine and also for mounting such an internal combustion engine on an automobile.
To cope with these problems, the Assignee of the present application earlier proposed a valve timing control device in Japanese Patent Unexamined Publication No. 2-185607, in which instead of hydraulic pressure, pneumatic pressure (negative intake pressure) is utilized. A comparison between this device and the device of the present invention is rather insignificant because the former utilizes the pneumatic pressure; however, in this conventional device, when the valve timing device is to be mounted on the internal combustion engine, "an air passage beak" constituting an air passage needs to be mounted at the same time, and therefore if they should be assembled together incorrectly, the degradation of the air-tightness can be confirmed only after the valve timing control device is mounted on the internal combustion engine, and therefore much time and labor are needed for repair or correction. And besides, because of the nature of such a construction, a seal device for the pneumatic pressure is exposed, and therefore when tightening a bolt for fixing a pneumatic actuator to an end portion of a camshaft, parts of the seal device may be damaged by a wrench.